The type checker's constraint solver

The constraint solver is at the core of GHC's type inference engine. This page is just to help me track some open stuff I'm working on.

Branch: wip/spj-solver-branch

TIckets concerning termination of the solver

• #12386 (closed) (only loosely related)
• #12522 (closed)
• #12526 (closed)
• #12444 (closed)
• #12538 (closed)